Digital measuring instrument having flexible measuring line

ABSTRACT

A digital tape measure includes a housing containing a measuring line, a rotatable measuring drum in engagement with the measuring line so that movement of the measuring line causes rotation of the measuring drum, and a rotatable disc coupled with the measuring drum for rotating simultaneously with the measuring drum. The digital tape measure includes an optical sensor in communication with the rotatable disk for compiling data related to rotation of the disk, and electronic circuitry in communication with the optical sensor for processing the compiled data so as to calculate a length of the measuring line drawn from the housing.

FIELD OF THE INVENTION

[0001] The present invention is related to tape measures used formeasuring distances and is specifically related to electronic tapemeasures.

BACKGROUND OF THE INVENTION

[0002] Tape measures have been used for many years to accurately measuredistances between two points and the lengths of objects. Tape measurestypically include a housing having an opening through which a measuringtape is drawn. The measuring tape has indicia printed thereon that areused to measure distances. When measuring a distance, the measuring tapeis unwound from a storage spool as it is drawn through the opening ofthe housing. When the measuring task is complete, the measuring tape isrewound onto the storage spool.

[0003] In recent years, electronic tape measures have been developedwhich electronically track the length of a measuring tape unwound from astorage spool. Electronic tape measures typically include a readingelement in communication with the storage spool that generates electricpulses corresponding to the length of the measuring tape drawn from thespool. The electric pulses are counted by operational circuitry, whichconverts the pulses into a digital readout provided on a visual display.

[0004] One electronic tape measure is disclosed in U.S. Pat. No.5,142,793 to Crane which teaches a housing, a reel located within thehousing and a measuring tape wound on the reel. The measuring tape isextendable through an opening in the housing as the reel is unwound. Afirst measuring element is associated with the reel for generatingincremental measuring data and a second measuring element generatesabsolute measuring data as the measuring tape is extended. A processorresponsive to both the incremental measuring data and the absolutemeasuring data generates an output that reflects the linear extension ofthe measuring tape from the housing. The device also includes a visualdisplay for showing information related to the linear extension of themeasuring tape.

[0005] U.S. Pat. No. 5,426,863 to Biggel discloses a combination tapemeasure and calculator. The tape measure includes a measuring tapehaving equally spaced holes along the length thereof. The holes are readby closely spaced optical readers arranged to generate incremental unitsignals that are transmitted to a microprocessor mounted in a case.

[0006] U.S. Pat. No. 5,433,014 to Falk et al. discloses a digital tapemeasure including a transmitter for transmitting measurements to aremote location. The tape measure includes a housing, a measuring tapehaving a series of optical markings, an optical sensor for sensing theoptical markings when the tape is extended or retracted, a logic circuitin communication with the optical sensor for providing a digital signalrepresentative of the length of the tape drawn from the housing, and atransmitter connected to the logic circuit for transmitting the digitalsignal to the remote location. A receiving unit is provided at theremote location for receiving, storing and displaying the measurements.

[0007] U.S. Pat. No. 5,286,972 to Falk et al. discloses a photoelectricmeasuring device with a digital display. The measuring device measuresdistance by optically scanning the length of a line as it is unwoundfrom a reel. The line is provided with a plurality of dye marks placedat spaced intervals. The dye marks are detected by an optical sensor incommunication with a circuit that maintains a count indicative of thelength of the line. The count is displayed on an LED display.

[0008] The above-described devices generally use measuring tapes havinga substantial width and thickness that limits the length of tape, suchas 100 meters or less, that can be conveniently stored on a singlespool. Tape measures having distances of over one hundred meters arerare because longer tapes will substantially increase the overall sizeof the tape measure housing, thereby making the tape measure extremelybulky and burdensome to operate.

[0009] Another problem with conventional tape measures relates tomaintenance and replacement costs. Tape measures are frequently damagedbecause they are used in harsh environments resulting in the measuringtape being damaged. A damaged measuring tape cannot accurately measure adistance or cannot be rewound onto a storage spool. As a result, themeasuring tape must be repaired or replaced at substantial cost. In manyinstances, a brand new tape measure must be purchased.

[0010] Another problem relates to the accuracy of electronic tapemeasures. Many conventional electronic tape measures are inaccurate orunreliable because they don't account for the hanging radius of themeasuring tape on the storage spool as the tape is unwound from thestorage spool.

[0011] Thus, there is a need for an electronic tape measure that enablesusers to measure longer distances. There is also a need for a durableelectronic tape measure, which allows the measuring element extendedfrom a housing to be easily replaced, at low cost. There is also a needfor an electronic tape measure that is accurate and reliable.

SUMMARY OF THE INVENTION

[0012] In accordance with certain preferred embodiments of the presentinvention, a digital tape measure includes a housing containing arotatable storage spool, and a measuring line windable about the storagespool. The tape measure also preferably includes a measuring drumrotatably mounted in the housing and including a surface in contact withthe measuring line, whereby movement of the measuring line causesrotation of the measuring drum. A disc is desirably coupled with themeasuring drum, whereby rotation of the measuring drum due to movementof the measuring line causes simultaneous rotation of the disc. Thedigital tape measure also includes an optical sensor in communicationwith the disc for compiling data related to rotation of the disc, andelectronic circuitry in communication with the optical sensor forprocessing the compiled data so as to calculate a length of themeasuring line drawn from the housing. The housing preferably includes avisual display, such as a digital display, adapted to show thecalculated length of the measuring line that has been drawn from thehousing.

[0013] The disc is preferably a circular disc that is rotatable about ashaft. The shaft preferably links the disc with the rotatable measuringdrum. The disc preferably includes a peripheral edge having a pluralityof evenly spaced teeth. The teeth desirably define evenly spaced gapstherebetween. When the disc is inserted into the housing of the digitaltape measure, the teeth of the disc are preferably in substantialalignment with the optical sensor. As a result, the rotating teeth arein alignment with the optical sensor.

[0014] The optical sensor of the present invention desirable includes alight generating element such as a light emitting diode, directed towarda first face of the rotating disc, and a light sensing element, such asa photo sensor, directed toward a second face of the disc. Thelight-generating element and the light sensing element preferably opposeone another and are in substantial alignment with one another. As thedisc rotates, the optical sensor generates a first signal when the lightfrom the light generating element reaches the light sensing element.When the disc rotates so that one of the teeth is aligned between thelight generating element and the light-sensing element, the opticalsensor generates a second signal indicating such a condition. As aresult, the optical sensor generates a first pulse signal when lightfrom the light generating element passes through one of the gaps betweenthe teeth of the disc to reach the light sensing element, and a secondpulse signal when light from the light generating element is blockedfrom reaching the light sensing element by one of the teeth of the disc.

[0015] The digital tape measure desirably includes a printed circuitboard including electronic circuitry in communication with the opticalsensor. The electronic circuitry is selected from the group consistingof analog circuitry and digital circuitry. The printed circuit boardalso preferably includes one of more microprocessors having one of moresubroutines stored therein for operating the electronic circuitry. Theelectronic circuitry preferably operates in conjunction with softwarethat enables a user to re-calibrate the unit for different types of linediameters and/or line materials. The calibration data is permanentlystored in memory, even when battery power is out and even if batterypower is not used. As a result, a user may change the measuring line touse a line having a different diameter or material, and thenre-calibrate the unit to work accurately with the new measuring line. Incertain preferred embodiments, the software is adapted to count pulsesfor a predetermined length of measuring line that passes the opticalsensor. In one particular preferred embodiment, the software is adaptedto count two (2) pulses for each 1 mm (0.04″) of measuring line, therebyensuring maximum precision and accuracy.

[0016] The measuring line drawn from the storage spool is preferablyflexible. In certain preferred embodiments, the measuring line is madefrom a material selected from the group consisting of cotton, metal andsynthetic materials such as nylon and polyester. In one preferredembodiment, the measuring line is string. In another preferredembodiment, the measuring line is made of stainless steel. The measuringline is wound about the storage spool and has a length of approximately750 to 1500 meters. Although not limited by any particular theory ofoperation, it is believed that using a measuring line, as opposed to awide measuring tape, enables a longer length of measuring material to bewound about a storage spool. As is well known to those skilled in theart, a conventional measuring tape has substantial thickness and widththat occupies a substantial amount of space on a storage spool. Thisdramatically limits the length of measuring tape that may be stored in ahand carried tape measure. In contrast, the present invention providesan elongated, flexible measuring line that has minimal width andthickness. As a result, a substantially longer length of material may bewound about a storage spool, thereby maximizing the distance that can bemeasured using the present invention.

[0017] In certain preferred embodiments, the housing includes ahingeable front cover having a button that may be depressed for allowingthe front cover to be swung from a closed position to an open position.In the open position, an interior region of the housing may be accessed.The present invention also desirably includes a crank assembly includinga crank handle. The crank assembly is coupled with the storage spool forproviding an element for rewinding the measuring line about the storagespool.

[0018] In certain preferred embodiments, the housing includes a welladapted to receive the storage spool and a removable cover securableover the well. The side cover includes a lock for selectively uncoveringthe well. As a result, a storage spool having worn or damaged measuringline wound about it may be replaced with another storage spool havingnew or repaired measuring line. Thus, the removable side cover enables areplacement storage spool with measuring line to be quickly and easilyinstalled in the housing.

[0019] The present invention also preferably includes a measuring drumassembly including the measuring drum, whereby the measuring drum ismounted on a shaft carrying a first gear that is mechanically coupledwith the rotating disc in communication with the optical sensor. Themeasuring line is threaded through the measuring drum assembly so thatmovement of the measuring line causes simultaneous rotation of themeasuring drum. Due to the gear and shaft linkages described above,rotation of the measuring drum causes simultaneous rotation of the disc.In certain preferred embodiments, the measuring drum includes at leastone stationary guide, at least one roller guide, and at least onecleaner guide for cleaning an exterior surface of the line. For example,if the measuring line is made of cotton, the cleaner guide may removeextraneous matter present at an outer surface of the measuring line.Thus, the measuring drum assembly defines a threaded path for themeasuring line as the measuring line passes between the storage spooland the opening in the hingeable front cover of the housing. Themeasuring drum assembly preferably maintains at least a section of themeasuring line in non-slip engagement with the surface of the measuringdrum, and maintains the measuring line under tension. As used herein,the term “non-slip surface” means that there will be no slippage betweenmovement of the measuring line and the outer annular surface of themeasuring drum.

[0020] Other preferred embodiments of the present invention disclose anelectronic measuring device having a flexible measuring line including ahousing having an opening for the measuring line, a storage spoolrotatably mounted in the housing for storing the measuring line, and ameasuring drum rotatably mounted in the housing and including a surfacein contact with the measuring line, whereby movement of the measuringline through the opening of the housing causes rotation of the measuringdrum. The electronic measuring device also desirably includes a disccoupled with the measuring drum for rotating simultaneously with themeasuring drum, an optical sensor in communication with the disc forgenerating signals related to rotation of the disc, and electroniccircuitry in communication with the optical sensor for processing thegenerated signals so as to calculate a length of the measuring linepassing through the opening of the housing.

[0021] Other preferred embodiments of the present invention include anelectronic tape measure comprising a housing adapted to store measuringline, the housing having an opening for drawing the measuring line fromthe housing, and a measuring drum mounted in the housing and including anon-slip surface in engagement with the measuring line, wherein movementof the measuring line rotates the measuring drum. The electronic tapemeasure also includes a disc coupled with the measuring drum forrotating simultaneously with the measuring drum, an optical sensor incommunication with the disc for recording data related to rotation ofthe disc, and electronic circuitry in communication with the opticalsensor for processing the recorded data so as to calculate a length ofthe measuring line passing through the opening of the housing. Thisparticular embodiment also preferably includes a storage spool rotatablymounted in the housing for receiving the measuring line, and a crankassembly connected with the storage spool for rotating the storage spoolso as to wind the measuring line about the storage spool.

[0022] Still other preferred embodiments of the present inventioninclude a digital tape measure having a housing containing a measuringline, and a rotatable measuring drum in engagement with the measuringline so that movement of the measuring line causes rotation of themeasuring drum. The digital tape measure also desirably includes arotatable disc coupled with the measuring drum for rotatingsimultaneously with the measuring drum, an optical sensor incommunication with the disc for compiling data related to rotation ofthe disc, and electronic circuitry in communication with the opticalsensor for processing the compiled data so as to calculate a length ofthe measuring line drawn from the housing. The optical sensor desirablyincludes a light-generating element opposed by a light-sensing elementthat is adapted to sense light emitted from the light-generatingelement. The optical sensor desirably generates a first signal whenlight from the light-generating element reaches the light-sensingelement, and a second signal when the light from the light-generatingelement is blocked by one of the teeth of the disc.

[0023] These and other preferred embodiments of the present inventionwill be described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 shows a side view of a digital tape measure, in accordancewith certain preferred embodiments of the present invention.

[0025]FIG. 2 shows a partially exploded view of the digital tape measureshown in FIG. 1.

[0026]FIG. 3 shows a cross-sectional view of the digital tape measureshown in FIGS. 1 and 2, including an optical sensor secured in ahousing.

[0027]FIG. 4 shows a front end view of the optical sensor shown in FIG.3.

[0028]FIG. 5 shows a bottom view of the optical sensor shown in FIG. 4.

[0029]FIG. 6 shows a sectional view of the optical sensor taken alongline VI-VI of FIG. 5.

[0030]FIG. 7A shows an exploded view of measuring drum assembly for adigital tape measure, in accordance with certain preferred embodimentsof the present invention.

[0031]FIG. 7B shows the measuring drum assembly of FIG. 7A in apartially assembled state with a measuring line threaded therethrough.

[0032]FIG. 7C shows a perspective view of the measuring drum assembly ofFIG. 7A in a fully assembled state.

[0033]FIG. 8 shows an expanded view of a stationary guide for ameasuring line, in accordance with certain preferred embodiments of thepresent invention.

[0034]FIG. 9 shows a top plan view of a control panel for a digital tapemeasure, in accordance with certain preferred embodiments of the presentinvention.

[0035]FIG. 10 shows a perspective view of the digital tape measure shownin FIG. 9.

[0036] FIGS. 11A-11B show subroutines for operational circuitry of adigital tape measure, in accordance with certain preferred embodimentsof the present invention.

[0037]FIG. 12 shows a schematic of electronic circuitry of used toperform the subroutines shown in FIGS. 11A-11B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0038]FIG. 1 shows a digital tape measure 20 including a housing 22having a front 24, a rear 26, atop a bottom 30. In certain preferredembodiments, housing 22 is made of molded plastic. Housing 22 includes ahingeable front cover 32 movable between open and closed positions.Hingeable front cover 32 includes a cutting element 36 attached theretofor selectively cutting or trimming a measuring line (not shown).Hingeable front cover 32 includes an opening 38 through which themeasuring line can be drawn from housing 22.

[0039] Housing 22 also includes a handle 40 that extends along rear 26between the top and bottom 28, 30 of housing 22. Handle 40 is preferablyintegrally molded with the housing 22. A gripping surface 42 ispreferably secured over an exterior surface of handle 40 for improvingthe gripability of the handle. The handle 40 also preferably includesone or more finger grooves 44 for enhancing a user's grip.

[0040] Housing 22 preferably includes a first molded part 46 and asecond molded part 48 that are assembled together and held together byscrews 50, 50A, 50B and 50C passed through openings 52A, 52B and 52Cformed in first molded part 46. Screws 50A-50C are preferably anchoredin threaded apertures (not shown) formed in second molded part 48 forreliably securing first and second molded parts 46, 48 together.

[0041] Housing 22 also preferably includes a battery compartment cover54 that selectively closes a battery compartment opening 55 at a lowerend of handle 40. Housing 22 also preferably includes a removable sidecover 56 that covers a well formed in housing 22 that is adapted toreceive a measuring line storage spool (not shown). Removable side cover56 includes a slidable lock 58 that may be urged towards a central knob60 for releasing side cover 56 from its attachment with housing 22.

[0042]FIG. 2 shows a partially exploded view of the digital tape measureof FIG. 1, after hingeable front cover 32 has been opened and side cover56 (FIG. 1) has been detached from housing 22. The well 62 is adapted toreceive a storage spool 64 having measuring line 66 wound thereon. Spool64 has a central opening 68 that is mounted over spool gear 69 having acentral shaft 70 and spaced projections 72 that are engageable withsimilarly shaped, spaced depressions (not shown) formed on an undersideof storage spool 64. The spaced projections 72 provide positivealignment of storage spool 64 with gear 74.

[0043] Digital tape measure 20 also includes a measuring drum assembly76 insertable into the front 24 of housing 22 when hingeable front cover32 is in the open position shown in FIG. 2. As will be described in moredetail below, measuring drum assembly 76 is designed to receive a freeend of measuring line 66 supplied from storage spool 64. Measuring drumassembly 76 includes a series of guides for threading the measuring line66 therethrough. Housing 22 also includes a stationary guide 78 havingan opening 80 extending therethrough for engaging and guiding themeasuring line 66 after the measuring line has passed through a frontend of measuring drum assembly 76.

[0044] The digital measuring tape also includes an optical sensor 82including a light generating element 84 and a light sensing element 86that are directed towards one another on opposite faces of a rotatabledisc 88 having teeth 90 at the periphery thereof and gaps 92 between theteeth 90. The teeth 90 are preferably evenly spaced from one another.

[0045] Hingeable front cover 32 includes a depressible button 96 and aprojection 98 integrally connected to button. When button 96 isdepressed, projection 98 moves in an arcuate path shown by arrow A₁.When hingeable front cover 32 is moved in a clockwise direction towardthe top 28 of housing 22, projection 98 is securable under locking bar100 for holding hingeable front cover 32 in the closed position. Inorder to open hingeable front cover 32 once again, button 96 isdepressed so as to uncouple projection 98 from engagement with lockingbar 100.

[0046] Digital measuring tape 20 also includes a printed circuit board102 secured within housing 22. The printed circuit board 102 preferablyincludes microelectronic elements (not shown) such as microprocessorsand memory devices for controlling electronic circuitry coupled withprinted circuit board 102. The printed circuit board 102 is preferablyin communication with optical sensor 82 for obtaining data from opticalsensor 82 when disc 88 rotates as measuring line 66 is drawn through theopening 38 of hingeable cover 32.

[0047] Referring to FIG. 3, digital tape measure 20 also includes abrake 104 having a pivotable brake knob 106 with an underside 108coupled with a first end 110 of a first lever 112. First lever 112 alsoincludes a lower end 114 coupled with a second lever 116. The secondlever 116 has a lower end with teeth 118 with teeth that mesh with crankassembly gear 120 having teeth 122. The brake knob 106 is pivotablebetween a first unlocked position and a second locked position. In thefirst unlocked position, the teeth 118 of second lever 116 are remotefrom the teeth 122 of crank assembly gear 120 so that crank assemblygear is free to rotate. In a second locked position shown in FIG. 3, theteeth 118 of second lever 116 engage the teeth 122 of crank handle gear120 so that crank handle gear 120 cannot rotate. In operation, the brake104 is movable back and forth between the first unlocked position andthe second locked position for selectively locking movement of the crankhandle gear 120.

[0048]FIG. 3 also shows rotatable disc 88 mounted in housing 22 forrotating in response to movement of a measuring drum, as will bedescribed in more detail below. The teeth 90 at the periphery of disc 88are designed to pass between light generating element 84 and lightsensing element 86 of optical sensor 82. Optical sensor 82 is preferablyin communication with printed circuit board 102 via communication line124.

[0049]FIGS. 4 and 5 show a front end view of optical sensor 82 includinglight generating element 84 and light sensing element 86. Disc 88 isprovided between light generating element 84 and light sensing element86. Disc 88 has a first face 126 facing toward light generating element84 and a second face 128 facing toward light sensing element 86. Theteeth 90 at the periphery of disc 88 are adapted to pass between thelight-generating element 84 and the light-sensing element 86 as disc 88rotates.

[0050]FIG. 6 shows the teeth 90 of disc 88 passing by light generatingelement 84. When one of the gaps 91 of disc 88 is aligned between thelight generating element and the light-sensing element, light generatedby light generating element 84 is able to pass through the gap 91 and besensed by light sensing element 86 (not shown). When one of the teeth 90is positioned between the light generating element and the light sensingelement, as shown in FIG. 6, the light emitted from the light generatingelement 84 is not sensed by the light sensing element. In operation,optical sensor 82 generates a first signal when the light passes throughone of the gaps 91 and a second signal when the light is blocked by oneof the teeth 90. The first and second signals are processed by theoperational circuitry to determine the length of the measuring linedrawn from the housing.

[0051]FIG. 7A shows an exploded view of a measuring drum assembly 76, inaccordance with certain preferred embodiments of the present invention.Measuring drum assembly 76 includes a base member 130 and a cap 132securable over the base member. The base member 130 includes a centrallylocated well 134 adapted to receive measuring drum 136 having an annularsurface 138 adapted to engage the measuring line unwound from thestorage spool (FIG. 2). The measuring drum 138 includes a central hub140 having an opening 142 adapted to receive shaft 144. Shaft 144 has alower end (not shown) passable through an opening 146 in the bottom ofwell 134 for supporting rotation of measuring drum 136, and an upper end148 having a drive gear 150 mounted thereon. The drive gear 150 rotatesat the same rate as measuring drum 136. A bearing 152, mountable at theupper end 148 of shaft 144 is insertable into a top wall aperture 154 ofcap 132.

[0052] Referring to FIGS. 2 and 7A, base member 130 includes an upstreamend 156 and a downstream end 158. When the measuring drum assembly 76 issecured within the housing 22, the upstream end 156 is positionedadjacent the stationary guide 78 and the downstream end 148 ispositioned adjacent the opening 38 of hingeable front cover 32 when thehingeable front cover is in the closed position. Base member 130includes a first stationary line guide 160 securable in U-shaped groove162 and a first line cleaner guide 164 securable in cup 166. Bottomassembly 130 also includes two roller guides 168, 170 for guidingmovement of the measuring line. Base assembly 130 also includes a secondstationary guide 172 securable in second U-shaped groove 174, a secondline cleaner guide 176 secured in a second cup 178 adjacent thedownstream end 158 of base member 130, and a third stationary guide 179between the second stationary guide 172 and second line cleaner guide176.

[0053]FIG. 7B shows measuring line 66 threaded through the base member130 of measuring drum assembly 76. The measuring line is drawn fromstorage spool 64. The measuring line is threaded in the followingpattern: first stationary line guide 160, first line cleaner guide 164,first roller guide 168, wrapped approximately one and two-thirds timesaround measuring drum 136, around second roller guide 170, throughsecond stationary line guide 174, through third stationary line guide175 and through second line cleaner guide 176 at downstream end 158. Themeasuring line 66 is then passed through the opening 38 in hingeablefront cover 32 (FIG. 3).

[0054] Referring to FIGS. 7A and 7C, after the measuring line 66 hasbeen threaded through the measuring drum assembly 76, the top cover 132and base member 130 are assembled together, such as by snap-fitting thetop cover 132 and base member 130 together. The fully assembledmeasuring drum assembly 76 is insertable into the front end of housing22 as shown in FIG. 2.

[0055]FIG. 8 shows an expanded view of the stationary guide 78 shown inFIG. 2. The stationary guide 78 includes an opening 80 that provides aguide for the measuring line (not shown) between the storage spool andthe upstream end 156 of measuring drum assembly 76 when the measuringdrum assembly is inserted into housing 22.

[0056]FIG. 9 shows a plan view of the top 28 of housing 22. The housing22 includes hingeable front cover 32 and depressable button 96 forenabling hingeable front cover to be swung away from a front end ofhousing 22. Hingeable front cover also includes opening 38 that enablesmeasuring line 66 to be drawn therethough.

[0057] The housing 22 has a visual display 180 such as a liquid crystaldisplay. Visual display 180 includes a main readout 182 providing asix-digit numeric with comma and decimal point for decimals. The mainreadout 182 provides current measuring line readings and displays thevalue of memory and recall locations. Visual display 180 also includes anegative sign 184 that is displayed when the value on the main readout182 is negative. The negative sign indicates that the measuring line isretracted from a “rezero” position. Visual display 180 also includes amemory indicator 186 that is displayed when memory is selected. Thememory indicator 186 indicates which of the 15 memory storage locationsis being used and when all of the 15 memory locations are “full.” Atthat point, a prompt “overwrite? Y/N” indicator 188 will illuminate. Ifa user desires to overwrite the previously stored memory at that memorylocation, the user will press the yes button below.

[0058] The visual display also includes a recall indicator 190 that isdisplayed when recall is selected. The recall indicator 190 indicatesthe last stored measurement and the corresponding memory location(1-15). Pressing the recall button again will step through to the nextmeasurement stored in memory. Visual display 180 also includes locationindicator 192 that displays the storage location of the saved value orthe recall value in memory. Visual display 180 also has a soundactivated indicator 194 that indicates when the sound function has beentoggled to the “on” position. Unit indicator 196 denotes the type ofunits that are being displayed in the main readout 182. Rezero indicator198 displays when the “On/Zero” button is pressed to rezero the display.Overwrite option indicator 188 is illuminated in the event that a userattempts to save a measurement in an occupied memory location. At thatpoint, the user is prompted to confirm the action with the overwriteoption indicator 188. Once a “yes” or “no” is selected, the overwriteoption indicator is turned off.

[0059] The visual display 180 also includes an add indicator,represented by the “+” sign 200, that confirms that the user is in the“add” mode. Low battery indicator 202 illuminates when battery voltageis below a predetermined level, such as 4.8 volts. Overspeed indicator204 illuminates when the digital tape measure will not function properlydue to the measuring line 66 moving at a speed of over 10 feet persecond. If the overspeed indicator 204 illuminates, a user shouldremeasure a length, while insuring that the measuring line does not moveat a speed of over 10 feet per second. The calibration indicator 206 isdisplayed when the “On/Zero” button is depressed and held for fiveseconds. At that point, the digital tape measure 20 enters calibrationmode.

[0060] Digital tape measure 20 also includes a series of data entry keysfor controlling operation of the device. The data entry keys include addbutton 208, Clear/No button 210, unit button 212, recall button 214,Enter/Yes button 216, sound activating button 218, memory storage button220 and On/Zero button 222. The housing 22 also includes brake button106 that may be toggled back and forth between a locked position and anunlocked position in which the measuring line 66 can be drawn from thehousing 22.

[0061] Referring to FIGS. 9 and 10, the tape measure also includes acrank assembly 224 having a crank handle 226 that is coupled with thestorage spool gear 69 for rotating storage spool 64 to wind measuringline 66 about storage spool 64. When the brake assembly 106 is movedinto the locking position, the crank assembly 224 is locked in place,thereby preventing further movement of the measuring line.

[0062]FIGS. 11A and 11B show preferred logic subroutines used foroperating the digital tape measure. FIG. 11 shows electronic circuitrymounted atop the printed circuit board (FIG. 2) for performing the stepsshown in the logic subroutines of FIGS. 11A and 11B.

[0063] Although the invention herein has been described with referenceto particular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the embodiments described herein and thatother arrangements may be devised without departing from the spirit andscope of the present invention as defined by the appended claims.

1. A digital tape measure comprising: a housing containing a measuringline; a rotatable measuring drum in engagement with said measuring lineso that movement of said measuring line causes rotation of saidmeasuring drum; a rotatable disc coupled with said measuring drum forrotating simultaneously with said measuring drum; an optical sensor incommunication with said disk for compiling data related to rotation ofsaid disk; electronic circuitry in communication with said opticalsensor for processing the compiled data so as to calculate a length ofsaid measuring line drawn from said housing.
 2. The digital tape measureas claimed in claim 1, wherein said optical sensor includes a lightgenerating element opposed by a light sensing element that is adapted tosense light emitted from said light generating element.
 3. The digitaltape measure as claimed in claim 2, wherein said disc has a plurality ofteeth at a peripheral edge thereof that pass between said lightgenerating element and said light emitting element during rotation ofsaid disc.
 4. The digital tape measure as claimed in claim 3, whereinsaid plurality of teeth are evenly spaced from one another by gapsextending therebetween.
 5. The digital tape measure as claimed in claim4, wherein said optical sensor generates a first signal when one of saidteeth blocks said light from reaching said light sensing element and asecond signal when said light is detected by said light sensing elementafter passing through one of said gaps.
 6. The digital tape measure asclaimed in claim 1, further comprising a storage spool mounted in saidhousing for securing said measuring line.
 7. The digital tape measure asclaimed in claim 6, wherein said storage spool is rotatable for windingand unwinding said measuring line from said storage spool.
 8. A digitaltape measure comprising: a housing containing a rotatable storage spool;a measuring line windable about said storage spool; a measuring drumrotatably mounted in said housing and including a surface in contactwith said measuring line, wherein movement of said measuring line causesrotation of said measuring drum; a disc coupled with said measuringdrum, wherein rotation of said measuring drum causes simultaneousrotation of said by disc; an optical sensor in communication with saiddisc for compiling data related to rotation of said disc; and electroniccircuitry in communication with said optical sensor for processing saidcompiled data so as to calculate a length of said measuring line drawnfrom said housing.
 9. The digital tape measure as claimed in claim 8,wherein said housing includes a digital display adapted to display thecalculated length of said measuring line drawn from said housing. 10.The digital measuring tape as claimed in claim 8, wherein said discincludes a peripheral edge having a plurality of teeth evenly spacedfrom one another.
 11. The digital measuring tape as claimed in claim 10,wherein said teeth define evenly spaced gaps therebetween.
 12. Thedigital measuring tape as claimed in claim 10, wherein said opticalsensor is in substantial alignment with said teeth of said disc.
 13. Thedigital measuring tape as claimed in claim 12, wherein said opticalsensor includes a light generating element directed toward a first faceof said disc and a light sensing element directed toward a second faceof said disc, wherein said light generating element and said lightsensing element oppose one another and are in substantial alignment withone another.
 14. The digital measuring tape as claimed in claim 13,wherein said disc is aligned with said light generating and lightsensing elements so that said teeth of said disc pass between said lightgenerating element and said light sensing element.
 15. The digitalmeasuring tape as claimed in claim 14, wherein said light generatingelement is a light emitting diode (LED) and said light sensing elementis a phototransistor.
 16. The digital measuring tape as claimed in claim15, wherein said phototransistor generates a first pulse signal whenlight from said light generating element passes through one of said gapsbetween said teeth of said disc and a second pulse signal when saidlight from said light generating element is blocked from reaching saidlight sensing element by one of said teeth of said disc.
 17. The digitaltape measure as claimed in claim 8, further comprising a printed circuitboard including said electronic circuitry.
 18. The digital tape measureas claimed in claim 17, wherein said electronic circuitry is selectedfrom the group consisting of analog circuitry and digital circuitry. 19.The digital tape measure as claimed in claim 8, further comprising amicroprocessor having one or more routines stored therein for operatingsaid electronic circuitry.
 20. The digital tape measure as claimed inclaim 8, wherein said measuring line is flexible.
 21. The digital tapemeasure as claimed in claim 8, wherein said measuring line is made of amaterial selected from the group consisting of cotton, metal syntheticmaterial, nylon and polyester.
 22. The digital tape measure as claimedin claim 8, wherein said measuring line is made of stainless steel. 23.The digital tape measure as claimed in claim 8, wherein said measuringline wound about said storage spool has a length of approximately750-1500 m.
 24. The digital tape measure as claimed in claim 8, whereinsaid housing includes a hingeable front cover having an opening forpassing said measuring line therethrough, said housing including ahandle integrally formed therewith.
 25. The digital tape measure asclaimed in claim 8, further comprising a crank handle coupled with saidstorage spool for winding said measuring line around said storage spool.26. The digital tape measure as claimed in claim 8, wherein said housingincludes a well adapted to receive said storage spool and a removableside cover attachable to said housing over said well.
 27. The digitaltape measure as claimed in claim 26, wherein said side cover includes alock for selectively uncovering said well.
 28. The digital tape measureas claimed in claim 8, further comprising a brake coupled with saidstorage spool for selectively locking said storage spool from rotating.29. The digital tape measure as claimed in claim 8, further comprising ameasuring drum assembly including said measuring drum, said measuringdrum being mounted on a shaft carrying a first gear, wherein said firstgear is mechanically coupled with a second gear which, in turn, iscoupled with said disc so that rotation of said measuring drum causesrotation of said disc.
 30. The digital tape measure as claimed in claim29, wherein said measuring drum assembly includes at least onestationary guide, at least one roller guide and at least one cleanerguide.
 31. The digital tape measure as claimed in claim 30, wherein saidmeasuring drum assembly defines a threaded path for said measuring lineas said measuring line passes between said storage spool and saidopening of said housing.
 32. The digital tape measure as claimed inclaim 31, wherein said measuring drum assembly maintains a section ofsaid measuring line under tension and in engagement with the non-slipsurface of said measuring drum.
 33. An electronic measuring devicehaving a flexible measuring line comprising: a housing including anopening for drawing said measuring line from said housing; a storagespool rotatably mounted in said housing for storing said measuring line;a measuring drum rotatably mounted in said housing and including asurface in contact with said measuring line, wherein movement of saidmeasuring line through the opening of said housing causes rotation ofsaid measuring drum; a disc coupled with said measuring drum forrotating simultaneously with said measuring drum; an optical sensor incommunication with said disc for generating signals related to rotationof said disc; and electronic circuitry in communication with saidoptical sensor for processing the generated signals so as to calculate alength of said measuring line passing through the opening of saidhousing.
 34. An electronic tape measure comprising: a housing adapted tostore a measuring line, said housing having an opening for drawing saidmeasuring line from said housing; a measuring drum mounted in saidhousing and including a surface in engagement with said measuring line,wherein movement of said measuring line rotates said measuring drum; adisc coupled with said measuring drum for rotating simultaneously withsaid measuring drum; an optical sensor in communication with said discfor recording data related to rotation of said disc; and electroniccircuitry in communication with said optical sensor for processing therecorded data so as to calculate a length of said measuring line passingthrough the opening of said housing.
 35. The electronic tape measure asclaimed in claim 34, further comprising: a storage spool rotatablymounted in said housing for receiving said measuring line; and a crankhandle connected with said storage spool for rotating said storage spoolso as to wind said measuring line about said storage spool.
 36. Theelectronic tape measure as claimed in claim 34, further comprising aprinted circuit board containing said electronic circuitry.
 37. Theelectronic tape measure as claimed in claim 34, wherein said electroniccircuitry is adapted to recalibrate for said measuring line when saidmeasuring line is made of different materials.
 38. The electronic tapemeasure as claimed in claim 34, further comprising data entry keys forcontrolling operation of said electronic circuitry.